Please describe how an acid-fast stain works. How does it get its name?

Answer 1

The term "Acid-fast" is a description of the bacteria and not the stain itself. Just like Gram-positive and Gram-negative stains are described by the characteristics of the bacteria. Acid-fast bacteria are a unique classification that have tough and waxy cell walls. They get their name from the mycolic acid component of their cell walls. Mycobacterium are the most famous (and perhaps only) type of bacteria that fit in this category. They cause diseases such as Tuberculosis and Leprosy.

Acid-fast staining hasn't really gained the same consistency in methods as gram-positive and gram-negative staining. Typically a lipid-soluble stain, such as carbolfuchsin, is used to help facilitate incorporation into the strongly hydrophobic cell wall. A counter-stain is also usually used to help distinguish between other cells in the culture that are not acid fast. Hope that helps!